1. Field of the Invention
This invention relates to a pumpdown, retrievable, subsurface, safety valve for use in a well.
2. The Prior Art
Subsurface, safety valves have been used in wells for some time. When vertical access to the well is available, subsurface, safety valves are generally installed and retrieved using wireline techniques. However, particularly on offshore wells where vertical access to the well is not practical, pumpdown equipment has been used to install or retrieve a subsurface, safety valve in the well.
Conventional subsurface safety valves have included a valve member movable between positions opening and closing the tubing bore to fluid flow. The valve member generally is adapted to move to a position opening the bore in response to fluid pressure. Biasing means are often provided to urge the valve member to a position closing the bore. For a surface conrolled, subsurface safety valve the baising means must overcome the force of the hydrostatic head of control fluid utilized to pressurize a pressure chamber. Because the force exerted by the hydrostatic head of fluid increases as the depth of the valve increases, the force exerted by the biasing means must also increase as the depth of the valve increases.
Springs are one common source of the biasing force for the biasing means. If the valves can be installed by wireline techniques, the biasing means can include a plurality of springs or one large spring. However, if the valve must be installed by pumpdown techniques, present safety valves have not been able to utilize a long spring or a plurality of springs to create the large force necessary to overcome a large hydrostatic head of fluid. This is because the valve must be pumped around a loop or short radius curvature before entering the well. A long valve simply connot be pumped through such a loop or curvature. Thus, pumpdown surface-controlled subsurface safety valves have been limited to the use of short springs to create the biasing force. Short springs have been unable to generate a sufficient amount of force to overcome the hydrostatic head of fluid for a valve positioned deep in the well.
Dome pressure chambers have also been used to create the biasing force. (See U.S. Pat. No. 3,860,066 to Pearce, et al). However, dome chambers also present problems. The seals of the dome chamber could fail resulting in a loss of pressure in the dome. This loss of dome pressure could render the valve totally inoperative, or worse yet, fail to close it.
The problems of present pumpdown, surface-controlled, subsurface, safety valves may be summarized as follows: because of the limitations on the valve length and the limited force that may be created by a short spring, if a spring is used as the biasing means the valves may only be used at shallow depths in the tubing. If a dome pressure chamber is utilized to generate the biasing force, possible leakage of pressure from the dome chamber results in less reliability and safety for the valve.
An injection, subsurface safety valve has similar problems. The biasing means must overcome the force of the hydrostatic head of fluid in the tubing. If a spring is used as the source of the biasing force, the pumpdown, subsurface injection safety valves have also been limited to the use of short springs with their inherent weakness. The reduced reliability of a dome pressure chamber also limits its use in a subsurface injection safety valve.
U.S. Pat. Nos. 3,891,032 to Tausch and 3,899,025 to Dinning disclose utilizing a ball joint in a pumpdown kickover tool body to allow the body to move through the curved portions of the pumpdown well tubing.